Viscoelastic Characteristics in Mouse Model of Hepatic Steatosis With Inflammation by Kelvin–Voigt Fractional Derivative Modeling

Objective: The aim of the work described here was to measure the characteristics of viscoelasticity and fluidity in a mouse model of hepatic steatosis and inflammation using a nano-indentation test and the Kelvin–Voigt fractional derivative (KVFD) model and to explore the viscoelasticity and fluidity characteristics in mice with different degrees of hepatic steatosis with inflammation. Methods: Twenty-five ApoE mice were randomly divided into an experimental high-fat diet group (n = 15) and an ordinary-food control group (n = 10), then subdivided into four subgroups based on pathological degree of hepatic steatosis: S0 (normal), S1 (mild), S2 (moderate) and S3 (severe). The 25 liver specimens from these mice were evaluated by a slope-keeping relaxation nano-indentation test. Results: Elasticity (E₀) was significantly higher in the S3 group than in the S1 and S2 groups, while fluidity (α) and viscosity (τ) were significantly lower in S3 than in S1 and S2 (all p values < 0.05). The following cutoff values for the diagnosis of hepatic steatosis >33% with inflammation were also determined: E₀ > 85.01 Pa (area under the curve [AUC]: 0.917, 95% confidence interval [CI]: 0.735–0.989), α ≤ 0.38 (AUC: 0.885, 95% CI: 0.695–0.977),\ and τ ≤ 3.92 (AUC: 0.813, 95% CI: 0.607–0.939). Conclusion: Increases in the degree of hepatic steatosis with inflammation in mice paralleled gradual increases in the stiffness of the liver and gradual decreases in the fluidity and viscosity of the liver.